Skewed fetal gender distribution in prolonged pregnancy: A fallacy with consequences

Abstract

Objective: Skewed gender distribution and falsely assigned gestational age lead to unnecessary or late obstetric intervention in prolonged pregnancy. The aim of this study was to examine the consequences of a fetal gender-dependent systematic 1.5-day dating error at ultrasound fetometry. Material and methods: A total of 82484 singleton deliveries ≥ 37 weeks at 11 hospitals in southern Sweden from 1995 to 2000 were included. Frequencies of labor induction and Apgar scores < 7 at 5 min were compared with regard to fetal gender, both before and after correction of gestational age by adding 0.75 days to female-fetus pregnancies and subtracting 0.75 days from male-fetus pregnancies. Results: The uncorrected odds ratio for having a male baby at ≥42 weeks was 1.41 (95% confidence interval, 1.33-1.49). After adjusting gestational age by ±0.75 days, the odds ratio reduced to 0.90 (95% confidence interval, 0.84-0.95). The risk for labor induction was significantly above unity in male-fetus pregnancies delivered after 41 weeks when gestational age was corrected for fetal gender, while the risk for female fetuses having a low Apgar score was not significantly increased compared to male fetuses (P = 0.087). Conclusion: Skewed gender distribution in prolonged pregnancy results in a higher rate of labor induction in pregnancies with male fetuses at ≤41 weeks, and the risk for newborn females having a low Apgar score in prolonged pregnancy is not significantly increased compared to boys. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.